Recently, demand for wireless communication service is increasing, which leads to a request to increase wireless communication system capacity. To increase the wireless communication system capacity, Multiple-Input Multiple-Output (MIMO) technology and scheduling technology for managing radio resources are suggested and developed.
Spatial Multiplexing (SM) and Space Division Multiple Access (SDMA) techniques are suggested as the representative of the MIMO technology, and standardized by 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and Mobile WiMAX. The SDMA technique increases the system capacity by concurrently sending a data stream to plurality of terminals per cell. Accordingly, how a base station effectively selects terminals to send the data at the same time from all of terminals requesting to send the data (that is, a scheduling method) greatly affects a system capacity gain according to the SDMA technique. Thus, the MIMO technology, particularly, the SDMA technique should be jointly optimized with the scheduling technique.
The scheduling technique in the wireless communication system enables the base station to select a terminal to send the data among the terminals requesting the data transmission. The scheduling should be designed to maintain fairness between the terminals in terms of the data transmission rate and to increase the system capacity.
A representative scheduling algorithm adopted in the wireless communication system is a Proportional Fair (PF) scheduling algorithm. The PF scheduling algorithm allows the terminal having the greatest ratio of an instantaneous transmission rate to an average transmission rate to send data using an instantaneous transmission rate information of each terminal fed back to the base station. Hence, since the data is transmitted to the terminal with the best instantaneous channel state compared to the average channel state, the system transmission capacity is raised and all of the terminals are given the transmission opportunity in the same number of times. As all of the terminals are given the transmission opportunity in the same number of times, the average transmission rate of each terminal is proportional to the average channel state of the corresponding terminal, which is referred to as proportional fairness between the terminals.
However, a PF scheduler, which ensures merely the proportional fairness between the terminals, cannot ensure a minimum required transmission rate for the service with respect to the terminals having low average received Signal to Interference and Noise Ratio (SINR). Further, the PF scheduler can offer the transmission opportunity over a maximum required transmission rate for the service to the terminals having a very good channel state.
In conclusion, in the downlink wireless communication system including MIMO antennas, a scheduling method and a scheduling apparatus are needed to control the fairness between the terminals and to control the transmission rate of the terminals according to the required transmission rate and the channel condition of the terminals.